Nowadays, the information recording technique, particularly the magnetic recording technique, requires a radical technological innovation following the development of the IT industry. For magnetic disks adapted to be mounted in magnetic disk apparatuses such as HDDs (hard disk drives), there is required a technique capable of achieving an information recording density of 60 Gbit/inch2 to 100 Gbit/inch2 or more. Hitherto, in a magnetic disk, a magnetic layer adapted to record information is provided on a nonmagnetic substrate and, on the magnetic layer, there are provided a protective layer for protecting the magnetic layer and a lubricating layer for reducing interference from a flying magnetic head. Further, there has heretofore been proposed a method of forming a protective layer by a plasma CVD method for ensuring the wear resistance and sliding properties of a magnetic disk (see, e.g. Patent Document 1).    Patent Document 1: International Publication No. 99/014746 Pamphlet